1. The Field of the Invention
This invention pertains to exercise equipment and, more particularly, to portable exercise devices and their use in providing safe, variable, constant and controlled resistance forces
2. The Background Art
Resistance exercise is used for both fitness and rehabilitation. Resistance is most commonly provided by either weights (free- or fixed) or elastic devices. When comparing the exercises performed with elastic resistance devices or weight devices, there is a similar activation/impact on muscle fibers, a similar increase in muscle strength and size, and similar decrease in body fat.
There are differences between weight and elastic exercise devices such as differences in size, weight, portability and cost. In addition, weight and elastic devices provide different patterns of resistance during any given range of motion. Weight-based exercise systems provide a constant force throughout the entire range of motion of an exercise movement. In contrast, elastic systems (due to the Hooke's Law relationship between distance and force) produce an increase in resistance as the range of motion increases. Both of these force characteristics may be either inefficient or potentially dangerous for either fitness or rehabilitation training.
Any particular joint movement possesses a torque versus joint angle curve, otherwise known as a strength curve. Strength curves result from the interaction of resistance and changing mechanical advantage of the musculoskeletal system during a range of motion. The strength curve of a joint is related to the length-tension relationship of muscles crossing the joint. The most common length-tension relationship in the human body produces an ascending-descending force curve. This curve indicates that during the early stages of any particular range of motion; the muscles, joints, and connective tissue may easily support a higher level of resistance but a lower level of resistance is all that can be tolerated in the later stages.
As a result, what is needed is a system, including an apparatus and method, capable of providing a free range of motion with sufficient but never excessive resistance at any given point during an exercise movement. The ability to control and modify the amount of resistance exerted by a device during each point of movement will optimize strengthening of muscles (resistance too low results in homeostasis) and also reduce risk of injuries (resistance too great results in structural failure). Resistance levels from either elastic or weight training systems should be controlled and modified during an exercise so that it conforms to the strength curve of the particular joint being utilized during the movement.
Numerous studies have been conducted that prove the benefit of “Compound” and “Free-Form” exercises. Free-form exercises are generally described as those that allow motion in multiple ranges and angles within the exercised joints capability and create instability for the user and require opposing (counter balancing) force to stabilize and balance the entire body during exercise movements. Compound exercises work several muscle groups at once, and often include the critical core muscles protecting the spine and internal organs. These exercises are generally similar to the ways that people naturally push, pull and lift objects, whereas isolation exercises often feel unnatural and are generally inefficient due to the number of isolation exercises required to train a multitude of muscles groups.
What is needed is a system, including an apparatus and method that is highly portable that can provide controlled resistance from a variety of angles affecting a multitude of joints and muscle groups simultaneously. This system, apparatus and method should provide variable, controlled resistance to efficiently enable concentric, eccentric and isometric muscle contractions to enable functional or natural training that mimics a body's complex movement in all three planes (sagittal, frontal and transverse).
Both elastic resistance (e.g. steel springs, elastic polymers) and free-weight resistance (e.g. barbells and dumbbells) have several similar properties. Both provide some form of resistance. However, configuration may affect range of motion, speed of movement, and progressive resistance. All these properties are useful in effective resistance-training programs.
Despite the similarities between elastic resistance and free-weight resistance, the lightweight appearance of elastic resistance equipment such as elastic tubing is deceiving. Studies have shown that muscle activity and peak load during elastic-resistance exercise is similar to free-weight resistance exercise.
This means that when comparing the same exercise performed with an elastic resistance device or with free weights, the amount of muscle fiber activated is similar. The amount of force provided by the muscle fibers is similar. Studies on elastic resistance training show an increase in muscle strength and muscle size and decrease in body fat in a manner to that of similar free-weight training programs.
A difficulty with free weights and weight-based exercise systems is that the force remains constant. That is, the weight never changes. On the other hand, in certain motions, the body may have greater or lesser leverage to support such a weight. Accordingly, muscles, joints, and connective tissue may actually have disproportionate forces exerted by virtue of the change in leverage advantage by a dead weight or free weight.
Meanwhile, a difficulty with elastic systems such as steel springs or elastomeric polymers is that the Hooke's Law relationship between distance and force results in an increase in force with each increase in distance. This may tend to over load muscles, joints, or both at the maximum extent of movement. Again, muscles, joints, and connective tissue may be over stressed due to the continuing increase in load as a bodily member passes through a particular distance.
Still needed is a system, including an apparatus and method, capable of providing a free range of motion of a bodily member. This may aid in rehabilitation as well as exercising for any particular activity. In addition to a free range of motion, such a system would benefit by providing an exercise regimen and a device that does not over stress joints in particular, nor over stress connective tissue and muscle throughout the range of operation.